The invention concerns the use of tires equipped with a safety insert and, in particular, detection of the bearing of a tire on the safety insert. It proposes an insert which warns the driver as soon as the tire is bearing on it after a flat or in case of substantial pressure loss, as well as a device for sensing the tire bearing on the insert, which can be combined with the insert proposed.
The function of these safety inserts, which are generally mounted on the rim inside the tire, is to bear load in case of failure of the tire.
Bearing of the tire on the safety insert is accompanied by a more or less marked deterioration of its performances, which can fail to be perceptible to the driver through the behavior of the vehicle and the discomfort of the passenger. Furthermore, the operating lifetime of these inserts is limited. It is therefore essential, for the driver""s safety, for the driver to be warned as soon as a tire is bearing on its safety insert, so that the driver can follow the manufacturer""s instructions.
Several safety inserts incorporating means for so warning the driver have previously been proposed.
U.S. Pat. No. 4,262,724 discloses a safety insert intended to be mounted in an assembly comprising a tire and a rim and radially on the outside of the rim. This insert has a radially outer surface which defines a radial bearing for the crown of the tire, when the tire is deflated, as well as means for generating vibrating warning signals on running flat. These means can be a variation of the rolling radius under bearing of the insert between a minimum radius and a maximum radius in order to create a rolling vibration or one or more bumps. All the vibrating warning signals generated by these means are oriented in the plane of the tire and rim assembly and, more specifically, in a roughly vertical direction.
These solutions pose several problems. In addition to marked discomfort for passengers of the vehicle, they can markedly degrade the performance of the tire and rim assembly concerned, particularly on acceleration and braking. Thus, all one can do is avoid instantaneous stoppage of the vehicle in case of failure of the tire. On the other hand, when it is desired to use the vehicle, even at limited speed, over long distances, the warning transmitted by the insert has to be compatible with driving safety, not detrimental to the mechanics, while remaining perfectly noticeable to the driver either directly or through a suitable detection device.
Patent application WO 94/03338 also proposes a device for the detection of the bearing of a tire on a safety insert. This device comprises a wheel accelerometer, placed on one of the wheel suspension elements and measuring vertical accelerations. The accelerometers are connected to a central processing unit. The analysis is based on detection of the appearance of a resonance mode characteristic of the run-flat condition.
The object of the invention is a safety insert which warns the driver, either directly or indirectly, upon bearing of the tire over a very wide range of speeds of the vehicle, while remaining tolerable to the driver and the mechanics within the speed limits.
The invention also concerns a device for detection of the bearing of a tire on its safety insert, which can, notably, cooperate with the safety insert according to the invention.
xe2x80x9cVehiclexe2x80x9d is understood below to be a self-contained rolling unit, passenger car, truck, tractor-trailer, motorcycle, etc.
xe2x80x9cRibxe2x80x9d refers to an element situated on the radially outer surface of a safety insert, of elongated shape, of roughly circumferential orientation and the radial height of which is less than or equal to the axial width: the ribs are xe2x80x9cstraightxe2x80x9d when their axial section is rectangular and xe2x80x9cinclinedxe2x80x9d when their axial section is in the shape of a parallelogram.
xe2x80x9cIncisionxe2x80x9d describes a similar element whose radial height is greater than the axial width.
The safety insert according to the invention, intended to be mounted in an assembly comprising a tire and a rim of a vehicle and radially on the outside of the rim, presents a radially outer surface which defines a radial bearing for the crown of the tire when it is deflated and means for generating vibrating warning signals on a run-flat condition. The said insert is characterized in that said means generate signals oriented parallel to the axis of rotation of the tire and rim assembly.
Said insert has two major advantages: the vibrating signals generated in the transverse direction are much more easily transmitted to the chassis and to the driver than similar vertically oriented signals. This is due to the excellent filtering carried out by the vehicle suspensions in the vertical direction in order to preserve the comfort of the passengers of the vehicle, while any transmission of stresses in the transverse direction is almost direct, with few filtering elements. On the other hand, those transverse vibrating signals degrade the performance of the tire and rim assembly in a straight line markedly less than those vertically oriented.
In a first embodiment of the invention, the bearing surface of the insert presents a variation of transverse direction according to its azimuth.
In a second embodiment, the bearing surface of the insert presents straight ribs, the circumferential orientation of which varies with their azimuth.
And in a third embodiment, the bearing surface of the insert presents elements generating a transverse stress on their radial compression.
This embodiment is particularly flexible. It is, in fact, possible to use inclined ribs or incisions relative to a longitudinal plane in variable manner according to their azimuth.
In a preferred variant, the safety insert according to the invention has a bearing surface with at least two axially adjacent zones, the zone intended to be placed outward from the vehicle not containing means for generating signals oriented parallel to the axis of rotation of the tire and rim assembly.
The latter solution has the advantage of preserving excellent turn performance of the tire and rim assembly upon running on a safety insert, In fact, on a turn, the tires placed outward from the turn are more loaded and usually take a marked counter-camber angle. Under such conditions, it is the xe2x80x9cinactivexe2x80x9d bearing zone (that is, not containing means for generating signals oriented parallel to the axis of rotation of the tire and rim assembly) which supports the bulk of the tire load without generating specific transverse vibrating signals. On the other hand, on a straight run, the tires have a much smaller camber angle and, the bearing zone containing means for generating transverse vibrating signals, the xe2x80x9cactivexe2x80x9d zone is then stressed.
The shape of the signal generated by the safety insert is also very important. The safety insert according to the invention preferably comprises a bearing with an active signal-generating zone, so that said signals present a maximum preceded and followed by a minimum in the opposite direction.
The active zone advantageously ranges between xc2xc and xc2xd the circumference of said insert and the absolute value of the minima of the signal generated ranges between xc2xc and xc2xe the absolute value of the maximum.
Such generated signals have the advantage of giving a spectrum of vibrations transmitted to the chassis of the vehicle on a run-flat condition in a well defined frequency band which favors precise and reliable detection.
The invention also concerns a first device for detection of the bearing of a tire of a vehicle, equipped with a plurality of tire, rim and safety insert assemblies mounted between the rim and the radially inner face of the tire tread, on the corresponding safety insert, each assembly being capable of triggering the emission of a vibrating signal, when the tire comes in contact with the insert after a pressure loss in the tire. Said detection device comprises means of detection and treatment of said vibrating signal, containing a single sensor capable of being mounted on the vehicle and sensitive to the signals emitted by each of the assemblies, when the corresponding tire comes in contact with the respective insert, and an indicator capable of signaling to the occupant of the vehicle a run-flat condition in response to a signal picked up by said sensor.
The characteristic vibrating signal is preferably maintained by the run-flat condition and can be emitted by a pressure-sensitive generator. Such a generator placed in the insert or on its surface is sensitive to any stress associated with the bearing of the tire tread on the insert and emits a signal, acoustic, for example, when that stress exceeds a given threshold. The acoustic signal can be easily picked up by a single receiver placed in the passenger space of the vehicle, connected to an indicator capable of warning the occupant of the vehicle of the run-flat condition.
The invention also concerns a second device for detection of bearing of a tire of a vehicle, equipped with a plurality of tire, rim and safety insert assemblies mounted between the rim and the radially inner face of the tire tread, on the corresponding safety insert, each assembly being capable of transmitting a characteristic vibration to the chassis of the vehicle in response to the bearing of one of the tires on the corresponding safety insert as a result of a pressure loss in the tire. This device comprises:
means of detection and treatment of such predetermined characteristic mechanical vibration of the chassis of the vehicle; and
means of transmission of an alarm.
This device presents the feature, by comparison with known devices, of making an analysis of the vibrations of the chassis of the vehicle instead of the suspension members.
As in the insert previously described, said device can preferably use direct paths of transmission of vibrations between the wheels and the chassis, in addition to vertical directions. Consequently, said device can be much more selective and sensitive than the existing devices and may have only one sensor rigidly connected to one of the parts of the chassis.
The device according to the invention is particularly well-suited to detection of bearing of a tire on a safety insert according to the invention, but it can also be used with any other insert, with or without vibrating means for alerting the driver to the bearing problem. In such case, it may be necessary to use two or more sensors measuring accelerations instead of only one. Each sensor is then preferably connected to one of the axles of the vehicle.
The means of treating vibrations of the chassis calculate a first characteristic magnitude in at least one given frequency band, they calculate a criterion C corresponding to a given combination of the preceding first characteristic magnitude or magnitudes, they compare that criterion C to a given threshold and they trip an alarm when the result of the comparison follows a given ratio.
Preferably, for each of the axles of the vehicle, the treatment means calculate a first characteristic magnitude in at least a first frequency band specific to the axle of the vehicle and calculate a criterion C corresponding to a weighted value of these first characteristic magnitudes.
The means of treating the vibrations of the chassis can also calculate, in addition, a second characteristic magnitude in a given second frequency band, so that, in said second band, said vibrations are appreciably independent of the bearing of the tire on its safety insert and deduce therefrom a criterion C corresponding to a value normed by that second characteristic magnitude of the first characteristic magnitudes, weighted or not.
According to a preferred embodiment, the treatment means further determine the frequency of rotation of the tire and said first frequency band or bands are narrow frequency bands, each centered on a multiple frequency of said tire rotation frequency. Those first frequency bands preferably range between 10 and 200 Hz.
The treatment centered on multiple frequencies of the tire rotation frequency very appreciably improves the sensitivity of bearing detection.
The characteristic magnitude calculated can be the rms values of the signals.
The invention also concerns a tire designed to equip a tire, wheel and safety insert assembly mounted between the rim and the radially inner face of the tire tread, characterized in that said tire is equipped with means capable of generating a vibrating signal, when said tire comes in contact with a corresponding insert following a pressure loss in said tire. These means can, for example, be a pressure-sensitive generator adhered to the inner surface of the tire.